Self-riveting male fastening elements of the type disclosed herein were first developed by Profil Verbindungstechnik GmbH & Co. KG of Germany, a company related to the assignee of the present application, as disclosed in U.S. Pat. No. 5,092,724. The fastening element includes a tubular or annular piercing and riveting portion or barrel portion which in the preferred embodiment pierced an opening in the panel which is then received through the panel opening into a die member having an annular concave die cavity. The die then deforms the free end of the barrel or riveting portion radially outwardly to permanently attach the fastening element to the panel. The fastening element further includes a radial flange portion which is driven into the panel as the free end of the tubular riveting portion is deformed radially outwardly forming a rigid secure installation in a panel. In the preferred embodiment, the fastening element further includes a male fastening portion integral with the radial flange or body portion coaxially aligned with the tubular riveting portion. Female fastening elements of this type were also developed, wherein the body portion includes an internal thread forming a nut-type fastener. Alternatively, the bore may be smooth to receive a self-rolling or self-tapping screw or bolt.
Self-attaching fastening elements of this type have been used extensively particularly in automotive and other applications requiring a secure rigid installation of a fastening element such as a stud, bolt, or nut in a metal panel or plate including body panels, brackets, structural elements and the like. However, self-piercing fastening elements of this type are generally limited to applications where the metal panel has a thickness generally less than about 2.5 mm or 0.098 inches. In automotive applications for example one problem solved by the self-piercing fastener disclosed in the above-referenced U.S. patent was to permanently attach a fastening element in relatively thin panels having a thickness of about 0.031 inches in a continuous operation. Later, fastening elements of this type were developed for permanent attachment of the fastening elements in relatively thick or heavy gauge metal panels as disclosed, for example, in U.S. Pat. Nos. 4,713,872; 5,237,733; and 5,564,873. In applications requiring the installation of a self-riveting fastening element of this type in heavy gauge metal panels having a thickness ranging from about 0.08 to 0.25 inches or greater, an opening configured to receive the tubular riveting portion of the fastening element is first formed in the panel. The tubular riveting portion of the fastening element is then received through the panel opening into a concave annular die cavity and the fastening element is then driven toward the die member which deforms the free end of the tubular riveting portion radially outwardly, permanently riveting the fastening element to the panel. The fastening element may include a radial flange portion which is driven into the panel to entrap the panel portion adjacent the panel opening and forming a flush mounting as disclosed in U.S. Pat. Nos. 5,237,733 and 5,564,873. Alternatively, the body portion may include a conical surface adjacent the tubular riveting portion forming a press fit as disclosed in U.S. Pat. No. 4,713,872. In the most preferred embodiment, however, the body portion includes a radial flange portion forming a more secure rigid fastener and panel assembly.
There are, however, problems in the installation of a self-riveting fastening element of the type described having a radial flange portion for installation in heavier gauge metal panels, particularly, but not exclusively male self-riveting fastening elements. A male self-riveting fastening element, for example, is driven toward the die member by a plunger having an annular end portion which surrounds the male fastening portion as disclosed in the above-referenced U.S. patents. The annular driving surface of the plunger is driven against an annular surface of the radial flange portion of the body portion of the fastening element which significantly deforms the radial flange portion during installation as shown in FIG. 9, described below, because of the force required for installation. As described in the above-referenced U.S. patents, self-riveting fasteners of this type are normally installed in a die press generating several tons of force and the die press may simultaneously form the plate or panel into a contoured shape. Several tons of force are required first to deform the free end of the tubular riveting or barrel portion radially outwardly in the concave arcuate annular die cavity, because of the extreme frictional resistance and large hoop stresses developed. These forces have been reduced by including an internal conical chamfer surface on the free end of the self-riveting portion and by friction resistant coatings; however, these approaches have not eliminated this problem. Further, the force required to deform the radial flange portion of the self-riveting fastening element into the panel results in further deformation of the radial flange portion during the final installation of the fastening element in the panel.
During installation of a self-riveting fastening element of the type described above, the radial flange portion is deformed by the driving surface of the plunger or ram toward and into the tubular riveting portion and radially, resulting in resulted in fewer structural integrity of the fastening element and panel assembly. This problem has reduced applications of this type of self-riveting fastening element in heavier gauge metal panels and problems following installation. As set forth below, this problem has been solved by the improved self-attaching fastening element of this invention by reducing the force required to install the self-riveting fastening element in a panel, thereby reducing the deformation of the radial flange portion during installation.